TWI742077B - Ammoxidation reactor control - Google Patents

Abstract

A process is provided for control of an ammoxidation reactor. More specifically, the process includes controlling an amount of oxygen added to the reactor, steam temperature and linear velocity to minimize reactor temperature deviations.

Description

Ammoxidation reactor control

Field of invention

A method of controlling an ammoxidation reactor is provided. More specifically, the method includes controlling the amount of oxygen added to the reactor, steam temperature, and linear velocity to minimize reactor temperature deviation.

Background of the invention

Acrylonitrile is produced by an ammoxidation method, in which air, ammonia, and propylene are reacted in a fluidized bed reactor in the presence of a catalyst. This is an exothermic reaction, and the heat generated is removed by circulating water or steam through a set of cooling coils that remove the heat to generate steam or superheated steam. The reactor temperature and reactor linear velocity are key variables, which need to be controlled to obtain the desired acrylonitrile yield. The reactor temperature is affected by the amount of propylene added to the reactor, reactor pressure, superheated steam temperature and the number of cooling coils used. The linear velocity is affected by the amount of propylene, ammonia and air added, and the pressure of the reactor. Cooling coil replacement is very common in acrylonitrile reactors. Coil replacement is usually performed by a process operator during rate changes or during a coil exchange process (a process of taking out coils that have been in use for a period of time and replacing them with new ones with better heat transfer capabilities).

It is desirable to operate the acrylonitrile reactor at the maximum possible linear velocity and at the fixed reactor temperature to obtain the best acrylonitrile yield. The main difficulty in achieving this goal comes from the fact that the cooling coils for a given reactor have different cooling capacities based on the number of passages they have. Therefore, the temperature response varies depending on the type of coil used to add or remove from the reactor. Traditional control schemes attempt to independently control the linear velocity and reactor temperature, and usually control actions in a reactive manner, especially during the replacement of the coil inside the reactor. This always increases the response time of the controller and takes a long time to stabilize the temperature after the coil is replaced. Therefore, the control scheme has to consider the interaction between key variables and take pre-control actions during coil replacement.

Summary of the invention

The ammoxidation method provides the maximum reactor linear velocity and the minimum deviation of the reactor temperature. Increased linear velocity and minimal reactor temperature deviation result in improved reactor efficiency.

The ammoxidation method includes introducing a reactant stream into an ammoxidation reactor. The reactant stream includes ammonia, oxygen-containing gas, and hydrocarbons selected from propane, propylene, isobutene, isobutene, and mixtures thereof. The method includes providing steam to a coil arranged in an ammoxidation reactor to provide a reactor operating temperature of about 350°C to about 480°C. The method also includes controlling the amount of oxygen added to the reactor and the temperature of the steam to maintain the apparent reactor linear velocity.

In another aspect, the ammoxidation method includes directing the reactant stream Into the ammonia oxidation reactor. The reactant stream includes ammonia, oxygen-containing gas, and hydrocarbons selected from propane, propylene, isobutene, isobutene, and mixtures thereof. The method includes providing steam to a coil arranged in an ammoxidation reactor to provide a reactor operating temperature of about 350°C to about 480°C. The method also includes controlling the amount of oxygen added to the reactor and the temperature of the steam to maintain the apparent reactor linear velocity within about 95% of the target apparent reactor linear velocity and within about 95% of the target reactor temperature .

The ammoxidation process introduces the reactant stream into the ammoxidation reactor. The reactant stream includes ammonia, propylene, and oxygen-containing gas. The method includes providing superheated steam to a superheating coil arranged in an ammoxidation reactor. In one aspect, the controlled variable group includes reactor oxygen flow, superheated steam temperature, absorber pressure, and the amount of lean water to the absorber, and the controlled variable group includes reactor linear velocity and reactor temperature. Controlling at least one controlled variable group includes controlling the amount of oxygen added to the reactor and the temperature of the superheated steam.

1, 2, 3‧‧‧Stream

4‧‧‧Reactor effluent stream

5‧‧‧Quench water flow

6‧‧‧Quench Flow

7‧‧‧Compressor effluent stream; effluent compressor stream

8‧‧‧Water Flow

9‧‧‧Effluent

10‧‧‧Reactor

11, 13, 15‧‧‧Pipeline

12‧‧‧Reactor shell; pipeline

14‧‧‧Air grid; pipeline

16‧‧‧Feeding sprayer; pipeline

17‧‧‧Saturated cooling coil; inlet

18‧‧‧Cooling system; water flow

19‧‧‧Superheated cooling coil; pipeline

20‧‧‧Cyclone separator; quench container

22‧‧‧Air inlet; cyclone separator

24‧‧‧Steam drum

25‧‧‧Dipping tube

26‧‧‧Effluent outlet; loop pump

28‧‧‧Block valve

30‧‧‧Steam control valve; compressor

32‧‧‧Steam inlet header

33‧‧‧Bypass pipeline; bypass passage

34‧‧‧Steam outlet header

35‧‧‧Steam supply pipeline

37‧‧‧Propylene control valve

39‧‧‧Controller

40‧‧‧Absorber

41‧‧‧Controller

44‧‧‧Catalyst bed

54‧‧‧Supplementary water pipeline

100‧‧‧Equipment

P1‧‧‧First pressure

P2‧‧‧Compression pressure

T ₁ 、T _R ‧‧‧Temperature

The above and other aspects, features and advantages of several aspects of the method are more apparent from the following drawings.

Figure 1 illustrates the equipment for the ammonia oxidation process.

Figure 2 illustrates the ammonia oxidation method.

In all the drawings, corresponding reference numerals indicate corresponding components. The skilled person should understand that the elements in the drawings are described for simplicity and clarity, and do not need to be drawn to scale. For example, the size of some elements in the drawings may be enlarged relative to other elements to help improve the understanding of various aspects. In addition, it usually does not describe general but familiar Known components to facilitate a less obstructive view of these various aspects.

Detailed description of the preferred embodiment

The following description should not be understood in a restrictive sense, but is only performed to describe the general principles of the exemplary embodiments. The scope of the present invention should be determined with reference to the scope of the patent application.

Ammonia oxidation reactor

Figure 1 illustrates a typical ammoxidation (acrylonitrile) reactor used. As shown, the reactor 10 includes a reactor shell 12, an air grid 14, a feed sprayer 16, a cooling system including a saturated cooling coil 17 and a superheated cooling coil 19 (which is generally indicated as 18), and a cyclone separator 20. Although Figure 1 shows that the saturated cooling coil 17 and the superheated cooling coil 19 are located on one side of the reactor 10, and the cyclone separator 20 is located on the other side, it should be understood that in actual operation these structures are uniformly arranged throughout the reactor . During normal operation, the method includes introducing a reactant stream, which includes ammonia, oxygen-containing gas, and hydrocarbons selected from propane, propylene, isobutene, isobutene, and mixtures thereof. In one aspect, the process air is charged into the reactor 10 through the gas inlet 22, and the mixture of propylene obtained from the propylene supply line 13 and ammonia obtained from the ammonia supply line 15 is charged into the reactor 10 through the feed sprayer 16. The flow rate of both is high enough to fluidize the ammoxidation catalyst bed 44 in the reactor, in which the catalytic ammoxidation of propylene and ammonia to acrylonitrile occurs. The flow rate of propylene to the ammoxidation reactor is effective to provide an oxygen:propylene ratio of about 2 to about 2.1 and an ammonia:propylene ratio of about 1 to about 1.5. The ammonia is controlled by the NH ₃ /C _{3 controller.}

The product gas produced by the reaction flows out through the reactor The product outlet 26 exits the reactor 10. Before that, they pass through the cyclone 20 to remove any ammonia oxidation catalyst that these gases may entrain, and return to the catalyst bed 44 through the dip tube 25. Ammoxidation is highly exothermic, so the cooling system 18 is used to recover excess heat and thereby maintain the reaction temperature at an appropriate level.

As further illustrated in FIG. 1, in addition to the saturated cooling coil 17 and the superheated cooling coil 19, the cooling system 18 also includes a steam drum 24, a loop pump 26, a shutoff valve 28 and a steam control valve 30. The lower part of the steam drum 24 is filled with saturated liquid cooling water and maintained at an elevated pressure and elevated temperature, for example, about 255° C., about 4.2 mPaG. The upper part of the steam drum 24 is filled with saturated steam in equilibrium with the liquid cooling water. As understood in the art, water exists as a liquid at these elevated temperatures because it is still at a pressure greater than one atmosphere.

The main way for the cooling system 18 to remove heat from the inside of the reactor 10 is to pass liquid cooling water from the lower part of the steam drum 24 through the cooling coil 17 and then circulate. For this purpose, a loop pump 26 is arranged to pump liquid cooling water from the bottom of the steam drum 24 through the shutoff valve 28 and then through the cooling coil 17. In the cooling coil 17, some of the liquid evaporates into steam, and the generated cooling water and steam are returned to the steam drum 24. Because the saturated cooling water fed to the cooling coil 17 consists of 100% liquid water, the cooling coil 17 is generally referred to as a "saturated" cooling coil.

In actual operation, the flow rate of the cooling water passing through the saturated cooling coil 17 is selected so that a predetermined proportion of the cooling water, for example, usually about 15%, is converted into steam. Therefore, as shown in Figure 1, the saturated cooling coil The heated cooling water generated in 17 returns to the upper part of the steam drum 24, so that the steam part of the cooling water flow can remain in the upper part of the steam drum, and the liquid part of the cooling water flow can fall to the lower part of the steam drum for communication with the steam drum 24. The liquid cooling water mixes there. The steam drum 24 may include a makeup water pipe 54.

In many designs, the shutoff valve 28 is a simple on-off valve, which is the opposite of a control valve that can fine-tune the fluid flow rate. This is because other equipment is usually used for fine-tuning the reaction temperature inside the acrylonitrile reactor, and therefore does not require more complicated and expensive control valves. It is also undesirable to convert a lot of liquid water into steam inside the cooling coil, as this can lead to adverse consequences, such as corrosion or fouling inside the cooling coil.

Each separate shut-off valve 28 on each separate coil is the only valve that controls whether the cooling water flows through the specific saturated cooling coil 17. In other words, the saturated cooling coil 17 is configured without any additional valves or other flow control devices for controlling the flow of cooling water passing through the saturated cooling coil 17. This is because such additional valves are not required to achieve the desired operation and control of the cooling coil in the manner described herein. In addition, removing the valve at the outlet also removes the need for a safety valve, which would be additionally required if such an outlet valve is used. Therefore, the total flow through all the working cooling coils (ie their valves are open to the saturated cooling coil 17) is set by the discharge flow rate of the pump 26.

In addition to the saturated cooling coil 17, the cooling system 18 also uses a superheated cooling coil 19 for removing heat from the inside of the acrylonitrile reactor 10. The superheated cooling coil 19 is different from the saturated cooling coil 17 because the superheated cooling coil 19 is connected to the upper part of the steam drum 24 through a steam inlet header 32 Section so that the feed to these cooling coils is superheated steam instead of saturated steam. The steam entering the superheated cooling coil 19 is at a saturation temperature corresponding to the pressure of the steam drum. As it flows through the hot steam coil 19 and thus becomes superheated, the steam drum pressure increases. Therefore, the cooling coil 19 is generally referred to as a "superheated cooling coil". In this aspect, the method includes providing superheated steam at a temperature of about 350°C to about 480°C, in another aspect, about 355°C to about 400°C, in another aspect, about 360°C to about 390°C, and On the other hand, it is about 370°C to about 380°C.

The important function of the superheated cooling coil 19 is to increase the temperature of the steam generated in the coil 19 to provide superheated steam for driving the steam turbine for other parts of the acrylonitrile plant, because the droplets in the wet steam may damage the interior of the turbine. For this purpose, the superheated steam sent from the superheated cooling coil 19 is usually discharged through the steam outlet header 34 to the steam supply pipe 35 for direct transfer to these steam turbines.

The usual operation in many acrylonitrile plants includes connecting the steam inlet manifold 32 and the steam outlet manifold 34 with a bypass line 33, so that the temperature of the steam passing into the steam supply pipe 35 can be directly supplied to the pipe from the steam drum 24 by adjusting Controlled by the amount of steam. Because the temperature of the steam in the steam drum 24 must be lower than the temperature of the superheated steam sent from the superheating cooling coil 19, increasing the steam flow rate through the bypass line 33 will inevitably reduce the temperature of the steam reaching the steam supply line 35. Therefore, it is also common in most industrial acrylonitrile plants to also include a steam control valve 30 in the bypass passage 33, the operation of which is controlled by the controller 39, in response to the steam measurement temperature T _{1 in the steam supply pipe 35} . Control valve 30 is then operated to maintain the measured temperature steam from the steam supply pipe 35 T ₁ somewhere constant at about 340-385 ℃.

In order to keep the acrylonitrile reactor operating under peak conditions, it is desirable to maintain its operating temperature within the target temperature range of about 200 to about 480°C, on the other hand, about 215 to about 440°C, and on the other hand, about 215-about 230°C, when using modern molybdenum-based ammoxidation catalysts. In this regard, it is more desirable to keep the reactor temperature as close as possible to a single control point temperature, rather than allowing the operating temperature to fluctuate within a certain temperature range. Although the control of the reaction temperature can be implemented by increasing or decreasing the number of working cooling coils, this method does not provide precise temperature control. Conversely, increasing or decreasing the cooling coil alone does not necessarily achieve an accurate reactor operating temperature.

Accordingly, precise temperature control acrylonitrile reactor 10 is typically carried out by increasing and decreasing the flow rate of propylene supplied to the reactor acrylonitrile, measuring its response to the temperature T _R ammoxidation reaction occurring inside the reactor is. For this purpose, as shown in FIG. 1, a propylene supply line 13 and a propylene control valve 37 in the controller 41 are provided to control the flow of propylene into the acrylonitrile reactor 10, which responds to the measured ammoxidation reaction temperature _TR . Therefore, a certain number of cooling coils are put into operation to provide reactor temperature control within the desired temperature range, and to adjust the propylene feed rate up and down to achieve more precise temperature adjustment.

In one aspect, the method provides improved temperature control and reduced reactor temperature deviation during changes in the heat transfer area of the coil. In this aspect, during the change of the heat transfer area of the coil, the reactor temperature deviation is maintained at about 10°C or less, on the other hand, about 6°C or less, and on the other hand, about 5°C or less , And in another aspect, about 3°C or less.

Each reactor can have a different target temperature within the range described herein. In one aspect, the amount of oxygen added to the reactor and the steam temperature are controlled to maintain the reactor temperature within about 95% of the target reactor temperature, and in another aspect, within about 98% of the target reactor temperature.

In another aspect, the total usable superheating coil area/reactor cross-sectional area (ft ² /ft ² ) is about 1 to about 7, in another aspect, about 2 to about 6, and in another aspect, about 3 -About 5. For each metric ton of acrylonitrile produced, the area of the superheating coil (ft ² )/the heat removed through the superheating coil (Kcal) is about 275,000 to about 475,000, on the other hand, about 300,000 to about 400,000, and in another On the one hand, 325,000-about 375,000.

In another aspect, the total usable saturated coil area/reactor cross-sectional area (ft ² /ft ² ) is about 8 to about 18, in another aspect, about 8 to about 15, and in another aspect, about 10 -Approximately 13. For each metric ton of acrylonitrile produced, the saturated coil area (ft ² )/heat removed by the superheating coil (Kcal) is about 2,375,000 to about 2,900,000, on the other hand, about 2,400,000 to about 2,800,000, and in another In terms of about 2,500,000 to about 2,700,000.

In one aspect, the method includes operating or reacting hydrocarbons in a reactor, wherein the effluent stream has a linear velocity of about 0.5 to about 1.5 meters per second, and in another aspect, about 0.7 to about 1.0 meters per second , On the other hand, from about 0.75 to about 0.8 m/sec, and on the other hand, from about 0.75 to about 0.77 m/sec (based on the effluent volumetric flow rate and reactor cross-sectional area excluding the area of the cooling coil and immersion tube Cross-sectional area ("CSA"), which is ~90% of the open CSA). It has been found that it is possible to use this speed to design and operate the reactor system while still obtaining good fluidization/catalyst performance and reasonable catalyst entrainment/catalyst loss from the cyclone separator, so that the speed can be increased to the extent possible to increase the reactor capacity. Stay near this range. In one embodiment, operable to maintain the reactor top pressure from about 0.25 to about 0.5kg / cm ^2, and in another aspect, from about 0.2 to about 0.45kg / cm ^2. On the other hand, the amount of oxygen added to the reactor and the temperature of the steam are controlled to maintain the apparent reactor linear velocity within about 95% of the target apparent reactor linear velocity, and on the other hand, in the target apparent reaction Within about 98% of the linear velocity of the machine.

In one aspect, the ratio of the cyclone inlet velocity (m/sec) to the reactor effluent velocity (m/sec) is 20 or greater, in another aspect, about 20 to about 30, and in another aspect, about 22 to about 25, in another aspect, about 23 to about 26, and in another aspect, about 27 to about 29.

In another aspect, the method includes controlling the reactor top pressure at about 3.8 psig to about 5.0 psig, in another aspect, 4.0 psig to about 5.0 psig, and in another aspect, about 4.0 to about 4.5 psig.

Figure 2 is a schematic flow diagram of an embodiment in accordance with aspects of the present disclosure for acrylonitrile production. With reference to this figure, the apparatus 100 includes a reactor 10, a quench vessel 20, an effluent compressor 30, and an absorber 40. The ammonia in stream 1 and the hydrocarbon (HC) feed in stream 2 may be fed to reactor 10 as combined stream 3. The HC feed stream 2 may include hydrocarbons selected from propane, propylene, and isobutene, and combinations thereof. A catalyst (not shown in FIG. 2) may be present in the reactor 10. The oxygen-containing gas can be fed to the reactor 10. For example, air may be compressed by an air compressor (not shown in FIG. 2) and fed to the reactor 10.

Acrylonitrile is produced in the reactor 10 from hydrocarbons, ammonia, and oxygen in the presence of a catalyst in the reactor 10. The reactor 10 can be in the reactor or the first pressure It runs under a force P1, where the first pressure can be characterized by the pressure at the inlet 17, such as the first stage inlet of the cyclone 22. According to the present disclosure, the cyclone separator 22 can be the first cyclone separator of a multi-stage cyclone separation system that can be configured to convey a stream containing acrylonitrile to a high pressure chamber (not shown in Figure 1). The stream containing acrylonitrile can leave the high-pressure compartment and exit the top of the reactor 10 as reactor effluent stream 4. In one aspect, the cyclone separator 22 may be configured to separate the catalyst that may be entrained in the acrylonitrile-containing stream entering the inlet 17, and return the separated catalyst to the immersion pipe (not shown in FIG. 1) through the catalyst return The catalyst bed in the reactor 10. The reactor effluent stream 4 produced in the reactor 10 containing acrylonitrile may be sent to the quench vessel 20 via the line 11. In this aspect, the first pressure is about 140 kPa or less, in another aspect, about 135 kPa or less, in another aspect, about 130 kPa or less, in another aspect, about 125 kPa or less, in another aspect, about 101kPa to about 140kPa, on the other hand, from about 110kPa to about 1400kPa, on the other hand, from about 125kPa to about 145kPa, on the other hand, from about 120kPa to about 140kPa, on the other hand, from about 130kPa to about 140kPa, in In another aspect, about 125 kPa to about 140 kPa, in another aspect, about 125 kPa to about 135 kPa, in another aspect, about 120 kPa to about 137 kPa, and in another aspect, about 115 kPa to about 125 kPa.

In the quench vessel 20, the reactor effluent stream 4 can be cooled by contact with the quenched aqueous stream 5 that enters the quench vessel 20 via line 12. In addition to water, the quenched aqueous stream 5 may contain acid. The cooled reactor effluent contains acrylonitrile (including by-products such as acetonitrile, hydrocyanic acid, and impurities) and can then be sent as quench stream 6 through line 13 to the effluent compressor 30.

The quench stream 6 may be compressed by the effluent compressor 30 and exit the effluent compressor 30 as the compressor effluent stream 7. Compressor effluent stream 7 may have a second or compression pressure P2. The compressor effluent stream 7 can be sent to the lower part of the absorber 40 through the line 14. In the absorber 40, acrylonitrile can be absorbed into the second or absorber aqueous stream 8, which enters the upper part of the absorber 40 through the line 15. The aqueous or rich water stream 18 including acrylonitrile and other by-products can then be transferred from the absorber 40 through line 19 to a recovery column (not shown in Figure 2) for further product purification.

The unabsorbed effluent 9 exits from the top of the absorber tower 40 through a pipe 16. The unabsorbed effluent 9 may contain exhaust gas, which may be burned in an absorber exhaust gas incinerator (AOGI) or an absorber exhaust gas oxidizer (AOGO).

In one aspect, the effluent compressor 30 operates by drawing the quench stream 6 through the line 13. The effluent compressor 30 can compress the quench stream 6 so that it leaves the effluent compressor 30 as a compressed effluent compressor stream 7, which has a higher pressure (the first pressure) than the reactor pressure (first pressure) Two pressure). In one aspect, the pressure of compressed effluent compressor stream 7 in line 14 is greater than the working pressure of reactor 10, from about 2 to about 11.5 times, on the other hand, from about 2 to about 12.5 times, in another In one aspect, about 2.5 to about 10, in another aspect, about 2.5 to about 8, in another aspect, about 2.5 to about 5, in another aspect, about 2.5 to about 4, and in another aspect, about 2.5 to about 8. About 3.2, in another aspect, about 2 to about 3.5, in another aspect, about 2 to about 3, in another aspect, about 3 to about 11.25, in another aspect, about 5 to about 11.25, and in another aspect on the one hand, About 7 to about 11.25 (all based on absolute pressure comparison). In one aspect, the second pressure (absolute pressure) is about 300 to about 500 kPa, in another aspect, about 340 kPa to about 415 kPa, in another aspect, about 350 kPa to about 400 kPa, and in another aspect, about 250 kPa to about 500 kPa In another aspect, about 200 kPa to about 400 kPa, in another aspect, about 250 kPa to about 350 kPa, in another aspect, about 300 kPa to about 450 kPa, and in another aspect, about 360 kPa to about 380 kPa.

In one aspect, the second pressure is such that when the water stream 8 is not cooled or refrigerated and/or is 4 to about 45° C., the absorber can operate at a flow rate of about 15 to about 20 kg/kg of the final product of acrylonitrile produced in the water stream 8 Operating below, and wherein the absorber rich water stream contains about 5% by weight or more organic matter, on the other hand, about 6% by weight or more organic matter, and in another aspect, about 7% by weight or more Of organic matter. In another aspect, the flow rate of the aqueous stream 8 may be about 15 to about 19 kg/kg of acrylonitrile, in another aspect, about 15 to about 18 kg/kg of acrylonitrile, and in another aspect, about 16 to about 18 kg/kg Acrylonitrile. In another aspect, the uncooled or uncooled aqueous stream is about 20 to about 45°C, in another aspect, about 25 to about 40°C, in another aspect, about 25 to about 35°C, and in another On the one hand, it is about 25 to about 30°C.

The cooling system (not shown in Figure 2) may be located at or downstream of the compressor 30, wherein the cooling system is configured to cool the compressed effluent compressor stream 7 to a predetermined temperature, for example, about 105°F (about 40.5°C) ), and then enter the absorber 40.

In one aspect, the absorber 40 may include forty to sixty (40-60) trays. In one aspect, the absorber may include fifty (50) towers plate. The compressed effluent compressor stream 7 may enter the absorber 40 below the bottom tray of the absorber. In one aspect, the absorber 40 can be operated at a variable flow rate of the refrigerating water in the second water-containing stream 8, including a refrigerating water volume of zero.

In one aspect, the absorber 40 may be operated at a higher pressure than that of the absorber in conventional methods. By operating the absorber 40 under this higher pressure, the absorber can be operated more efficiently than the absorber in the conventional method. Due to the higher absorber efficiency obtained in the method of the present disclosure, the same recovery rate of acrylonitrile in the rich water stream 18 can be obtained as in the conventional method, but less water is required to absorb acrylonitrile in the absorber . In this aspect, rich water refers to water having about 5% by weight or more organic matter, on the other hand, about 6% by weight or more organic matter, and in another aspect, about 7% by weight or more Organic matter. In one aspect, the water used to absorb acrylonitrile in the absorber may be process water or city water (e.g., having a temperature of about 4-45°C). In this aspect, process water or city water is more than about 95% by weight water, in another aspect, about 97% by weight or more water, in another aspect, about 99% by weight or more water, and On the other hand, about 99.9% by weight or more water. In one aspect, the temperature of the second aqueous stream may be about 4 to about 45°C, in another aspect, about 10 to about 43°C, and in another aspect, about 27 to about 32°C.

Advanced process control

Model predictive control (MPC), also known as advanced process control (APC), uses process models to predict future process behavior, and then performs optimal control actions to calculate process deviations based on desired goals. Together with the control process, MPC also tries to drive the process to The most "economic" conditions. One aspect of this method includes MPC to control the reactor temperature and linear velocity. The method includes the use of MPC to achieve the maximum linear velocity possible for the reactor and a constant reactor temperature with minimal deviation during coil changes.

As used herein, the term "manipulated variable" refers to a variable adjusted by an advanced process controller. The term "controlled variable" refers to a variable that is maintained within a predetermined value (set point) or a predetermined range (set range) by a high-level program controller. "Optimizing a variable" refers to maximizing or minimizing the variable and keeping the variable at a predetermined value.

One aspect of model predictive control is the use of available measurements of models and controlled variables to predict future process behavior. The controller output is calculated to optimize the performance index, which is a linear or quadratic function of the predicted error and the calculated future control action. At each sampling time, the control calculation and the updated forecast based on the current measurement result are repeated. In this regard, a suitable model is a model including a set of empirical step response models that express the influence of the step response of the manipulated variable on the controlled variable.

The optimal value of the parameter to be optimized can be obtained by a separate optimization step, or the variable to be optimized can be included in the performance function.

Before the model predictive control can be applied, first determine the influence of the step change of the control variable on the variable to be optimized and on the controlled variable. This results in a set of step-response coefficients. This set of step-response coefficients forms the basis of the model predictive control of the process.

During normal operation, predictive values of controlled variables are regularly calculated for some future control actions. Computing performance indicators for these future control actions number. The performance index includes two items, the first item represents the sum of future control actions for the prediction errors of each control action, and the second item represents the sum of future control actions for the change of the control variable of each control action. For each controlled variable, the prediction error is the difference between the predicted value of the controlled variable and the reference value of the controlled variable. The prediction error is multiplied by the weighting factor, and the change in the control variable for the control action is multiplied by the action suppression factor. The performance index discussed here is linear.

Alternatively, these terms may be the sum of square terms, in which case the performance index is quadratic. In addition, you can set constraints on manipulation variables, manipulation variable changes, and controlled variables. This results in an independent system of equations that is solved while minimizing the performance index.

Optimization can be performed in two ways: one way is to optimize separately in addition to the performance index minimization, and the second way is to optimize within the performance index.

When optimizing alone, the variable to be optimized is included as a controlled variable in the prediction error for each control action, and the optimization generates the reference value of the controlled variable.

Alternatively, optimization is performed within the performance index calculation, and this results in the third term in the performance index with an appropriate weighting factor. In this case, the reference value of the controlled variable is a predetermined steady-state value, which remains constant.

Considering constraints, the performance index is minimized to obtain the control variable value for future control actions. However, only the next control action is executed. Then start the calculation of the performance index again for future control actions.

The model with step response coefficients and the equations required in the model predictive control are part of the computer program, which is executed to control the liquefaction process. A computer program loaded with such a program that can handle model predictive control is called an advanced program controller. Available commercially available computer programs include, for example, Aspen Technology of DMCplus ^® and Emerson's PredictPro ^®.

Although the invention disclosed herein has been described through specific embodiments, examples and their applications, those skilled in the art can make many improvements and changes to it without departing from the scope of the invention as set forth in the scope of the patent application.

1, 2, 3‧‧‧Stream

4‧‧‧Reactor effluent stream

5‧‧‧Quench water flow

6‧‧‧Quench Flow

7‧‧‧Compressor effluent stream; effluent compressor stream

8‧‧‧Water Flow

9‧‧‧Effluent

10‧‧‧Reactor

11, 13, 15‧‧‧Pipeline

12‧‧‧Reactor shell; pipeline

14‧‧‧Air grid; pipeline

16‧‧‧Feeding sprayer; pipeline

17‧‧‧Saturated cooling coil; inlet

18‧‧‧Cooling system; water flow

19‧‧‧Superheated cooling coil; pipeline

20‧‧‧Cyclone separator; quench container

22‧‧‧Air inlet; cyclone separator

24‧‧‧Steam drum

30‧‧‧Steam control valve; compressor

40‧‧‧Absorber

100‧‧‧Equipment

P1‧‧‧First pressure

P2‧‧‧Compression pressure

Claims (35)

An ammoxidation method, comprising: introducing a reactant stream into an ammoxidation reactor, wherein the reactant stream comprises: ammonia, an oxygen-containing gas, selected from propane, propylene, isobutene, isobutylene and their The mixture of hydrocarbons; and steam is provided to the coil arranged in the ammoxidation reactor to provide a reactor operating temperature of about 350°C to about 480°C, wherein the amount of oxygen added to the reactor is controlled and Steam temperature to maintain the apparent reactor linear velocity. The method of claim 1, wherein the apparent reactor linear velocity is maintained at about 0.5 m/s to about 1.5 m/s. The method of claim 2, wherein the apparent reactor linear velocity is maintained at about 0.7 m/s to about 1.0 m/s. The method of claim 3, wherein the apparent reactor linear velocity is maintained at about 0.75 m/s to about 0.80 m/s. The method of claim 1, wherein the temperature deviation of the reactor is maintained at about 10°C or less during the change of the heat transfer area of the coil. The method of claim 1, wherein the steam is superheated steam and the coil is a superheated coil. The method of claim 6, wherein the superheated steam is provided at a temperature of about 355°C to about 400°C. The method of claim 1, wherein the pressure at the top of the reactor is maintained at about 3.8 psig to about 5.0 psig. The method of claim 6, wherein the total usable superheating coil area/reactor cross-sectional area (ft ² /ft ² ) is about 1 to about 7. The method of claim 9, wherein for every metric ton of acrylonitrile produced, the area of the superheating coil (ft ² )/the amount of heat removed through the superheating coil (Kcal) is about 275,000 to about 475,000. The method of claim 1, wherein the reactant stream includes propylene. The method of claim 11, wherein the flow rate of propylene to the ammoxidation reactor is effective to provide an oxygen:propylene ratio of about 2 to about 2.1 and an ammonia:propylene ratio of about 1 to about 1.5. The method of claim 1, further comprising sending the reactor effluent to the absorber, wherein the absorber has a pressure of about 35 psig to about 40 psig. An ammoxidation method, comprising: introducing a reactant stream into an ammoxidation reactor, wherein the reactant stream comprises: ammonia, an oxygen-containing gas, a hydrocarbon selected from propane, propylene, isobutylene, isobutylene, and mixtures thereof; and Steam is provided to the coil arranged in the ammoxidation reactor to provide a reactor operating temperature of about 350°C to about 480°C, wherein the amount of oxygen added to the reactor and the steam temperature are controlled, and the meter is maintained The apparent reactor linear velocity is within about 95% of the target apparent reactor linear velocity and maintained within about 95% of the target reactor temperature. The method of claim 14, wherein the apparent reactor linear velocity is maintained within about 98% of the target apparent reactor linear velocity. Such as the method of claim 14, wherein the transmission of the coil During the thermal area change, the reactor temperature deviation was maintained at about 98% of the target reactor temperature. The method according to claim 14, wherein the steam is superheated steam and the coil is a superheated coil. The method of claim 17, wherein the superheated steam is provided at a temperature of about 355°C to about 400°C. The method of claim 14, wherein the reactor pressure is maintained at about 3.8 psig to about 5.0 psig. The method of claim 17, wherein the total usable superheating coil area/reactor cross-sectional area (ft ² /ft ² ) is about 1 to about 7. Such as the method of claim 20, wherein for each metric ton of acrylonitrile produced, the area of the superheating coil (ft ² )/the amount of heat removed through the superheating coil (Kcal) is about 275,000 to about 475,000. The method of claim 14, wherein the reactant stream includes propylene. The method of claim 22, wherein the flow rate of propylene to the ammoxidation reactor is effective to provide an oxygen:propylene ratio of about 2 to about 2.1 and an ammonia:propylene ratio of about 1 to about 1.5. The method of claim 14, further comprising sending the reactor effluent to the absorber, wherein the absorber has a pressure of about 35 psig to about 40 psig. An ammoxidation method, which comprises: introducing a reactant stream into an ammoxidation reactor, wherein the reactant stream comprises: ammonia selected from propane, propylene, isobutylene, isobutylene and their Mixture of hydrocarbons, and oxygen-containing gas; provide superheated steam to the superheating coil arranged in the ammoxidation reactor; and wherein the control variable group includes reactor oxygen flow, superheated steam temperature, absorber pressure and to the absorber The controlled variable group includes the linear velocity of the reactor and the reactor temperature, wherein controlling at least one controlled variable group includes controlling the amount of oxygen added to the reactor and the temperature of the superheated steam. The method of claim 25, wherein the method includes controlling the apparent reactor linear velocity and the reactor operating temperature based on the model predictive control to determine the synchronous control action of the manipulated variable, so as to optimize at least one parameter group while controlling at least one Controlled variable array. The method of claim 26, wherein the method provides a reactor linear velocity of about 0.5 m/s to about 1.5 m/s. The method of claim 27, wherein the method provides a reactor linear velocity of about 0.7 m/s to about 1.0 m/s. The method of claim 28, wherein the method provides a reactor linear velocity of about 0.75 m/s to about 0.80 m/s. The method of claim 25, wherein the reactor pressure is maintained at about 3.8 psig to about 5.0 psig. The method of claim 25, wherein the method provides a reactor temperature deviation of about 10°C or less during the change of the heat transfer area of the superheating coil. Such as the method of claim 31, wherein the transmission of the coil During the thermal area change, the reactor temperature deviation is maintained at about 5°C or less. The method of claim 25, wherein the superheated steam has a temperature of about 355°C to about 400°C. The method of claim 25, wherein the flow rate of propylene to the ammoxidation reactor is effective to provide an oxygen:propylene ratio of about 2.0 to about 2.1 and an ammonia:propylene ratio of about 1 to about 1.5. The method of claim 25, further comprising sending the reactor effluent to the absorber, wherein the absorber has a pressure of about 35 psig to about 40 psig.

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